1. Field of the Invention
The present invention relates generally to a vehicle lamp lighting-driving apparatus, and more particularly to a vehicle lamp lighting-driving apparatus wherein a lamp is lighted by the use of a battery power source having a voltage higher than a required voltage of the lamp.
2. Description of the Related Art
A battery having a voltage of 12 volts (hereinafter xe2x80x9cVxe2x80x9d) is generally used as a vehicle carried battery power source. However, because there are a lot of vehicle applied devices which require a voltage higher than 12V for effective operation, and also the higher voltage enables a power feeder to be thinner, a high-voltagization of a power source has begun to be studied recently.
There exist, however, loads which are difficult to be operated with a higher voltage. As one of the above loads, there exists a lamp. In case of a lamp, when a battery power source of a higher voltage is used, a power consumption thereof increases due to its current increase. Besides, deterioration or a melt-breaking of a filament of the lamp, caused by generation of heat, would arise.
For example, in case that the voltage of a battery power source for a lamp is raised to
3 times and the resistance value of the lamp is below 9 times, the power consumption increases. A filament shall be lengthened in order to make the resistance value 9 times, which requires a shape of the filament and therefore a shape of a reflector to be changed. Like this, it would not be easy to obtain a lamp suitable to a higher voltage.
Therefore, carrying a plurality of battery power sources including a generally used 12V battery power source has also begun to be studied so as to apply a generally used 12V lamp. In such a case, however, a voltage raising means or a voltage lowering means for an alternate voltage generated by an alternator is also required. Therefore, to lighting-drive a generally used 12V lamp by the use of the battery power source having the higher voltage is being studied.
Japanese Patent Application Laid-open No.5-168164 discloses a lamp lighting-driving apparatus (FIG. 5), wherein a battery power source of an effective voltage of 42V is applied to a lamp having a required voltage of 12V.
As shown in FIG. 5, a battery power source (not illustrated) of the effective voltage 42V is applied to the lamp 27 through a FET (i.e. field-effect transistor) 28. On/off-driving of the FET 28 is carry out through a resistance R2, a transistor 29-1, and a resistance R3, based on a pulse driving signal generated by a driving signal generation portion 25(a). The period of the pulse forming the pulse driving signal is set to a time period not allowing recognition of on-and-off of the lamp 27.
The driving signal generating portion 25(a) watches a state of a switch 26 connected to an input terminal 21 for lighting the lamp installed on a vehicle operating panel, and generates and outputs the pulse driving signal from an output terminal 22(a) while the switch 26 is closed.
The above pulse driving signal is outputted so that a duty factor thereof is the same as that of the case wherein the lamp 27 is lighted with the usual 12V. Because the battery power source of the effective voltage of 42V applies a voltage of 36V to the lamp 27. That is, a voltage of 3 times the usual 12V is applied to the lamp.
In such a case, the power consumption of the lamp 27 becomes 9 times. Then, as shown in FIG. 6, a duty factor t1/t2 is set to 1/9 to shorten duration of a current to the lamp 27 and to equalize a power consumption to the case of driving the lamp 27 with 12V.
At a timing of the output from the output terminal 22(a) being High, a current flows to the resistance R4 and a voltage is generated between base-collector of the transistor 29-1. Accordingly, the transistor 29-1 becomes an ON state because a resistance value between base-emitter of the transistor 29-1 becomes smaller in comparison with a resistance value at a timing of the output from the output terminal 22(a) being Low. At this time, the FET 28 is on-driven because a voltage is generated between source-gate of the FET 28 by means of a voltage drop due to a current flowing through the resistance R1. And, a current flows to the lamp 27 connected to the drain of the FET 28.
At a timing of the output from the output terminal 22(a) being Low, the transistor 29-1 becomes an OFF state because a resistance value between base-emitter of the transistor 29-1 becomes large in a degree capable of ignoring the resistance R1. At this time, because a current does not flow to the resistance R1, a voltage drop is not generated. Accordingly, the FET 28 becomes an OFF state because the voltage is not generated between source-gate of the FET 28, and a current does not flow through the lamp 27.
With the above apparatus, because the lamp 27 consumes electric power while the FET 28 is on-driven, the power consumption of the lamp 27 is the same as that of the case of the 12V battery power source. And, an effective value of the current flowing through the cable for applying the voltage to the FET 28 can be decreased.
With respect to the structure shown in FIG. 5, however, a current exceeding the rated current of the lamp 27 suddenly flows thereto just after the voltage is applied to the lamp 27, which causes to shorten lifetime of the lamp 27. The current exceeding the rated current is called a rush current.
A resistance value of the lamp 27 is extremely small while the temperature is low, and therefore the rush current flows just after the voltage has been applied to the lamp 27. Upon generation of heat by the lamp 27, the resistance value of the lamp 27 increases, which lowers a current flowing to the lamp 27.
Upon cutting the current to the lamp 27, the lamp 27 stops generating heat, and the temperature goes down, which lowers the resistance value of the lamp 27. When the voltage is applied again to the lamp 27 subsequently the above, the rush current also flows to the lamp 27. However, because the temperature of the lamp 27 itself rises, the level of the rush current is lowered.
FIG. 6 is a timing chart showing the details of operation of the prior art vehicle lamp lighting-driving apparatus. On closing the switch 26, the driving signal generating portion 25(a) detects voltage at the input terminal 21 and outputs the pulse driving signal from the output terminal 22(a). The pulse driving signal continues to be outputted until the voltage at the input terminal 21 is not detected.
When a current begins to flow to the lamp 27, the rush current 31 flows as shown in FIG. 6. The rush current 31 repeatedly flows into the lamp 27 at a timing of High-level of the pulse driving signal outputted from the driving signal generating portion 25(a) until the temperature of the filament of the lamp 27 rises enough.
Because the rush current 31 is in proportion to the voltage applied to the lamp 27, the higher the voltage of the battery power source is, the larger the rush current is. The lifetime of the lamp 27 is shortened by the repeated large rush current 31.
In view of the foregoing, an object of the present invention is to provide a vehicle lamp lighting-driving apparatus, wherein a lamp, which is lighted by the use of a battery power source having a voltage higher than a rated voltage of the lamp, is driven with a pulse having a duty factor to make a power consumption of the lamp be a rated value and deterioration of the lamp is prevented by controlling an occurrence of a rush current to the lamp.
In order to achieve the above-described object, as a first aspect of the present invention, a vehicle lamp lighting-driving apparatus as shown in FIG. 1 comprises: a lighting driving means 3 to lighting-drive a lamp 27; a driving signal generating means 5 to generate a pulse driving signal having a pulse with a duty factor to make a power consumption of the lamp 27 be a rated value of the lamp; and a driving controlling means 4 to on/off-drive the lighting driving means 3 according to the pulse driving signal, wherein the driving signal generating means 5 generates an auxiliary driving signal which makes the driving controlling means 4 control the lighting driving means 3 so that a current to flow to the lamp 27 through the lighting driving means 3 is limited for a definite time, until a rush current at a time of on-driving of the lighting driving means 3 gets equal to or smaller than an allowable value, prior to the pulse driving signal at a start of lighting the lamp 27.
According to the above vehicle lamp lighting-driving apparatus, the lamp 27 can be lighted with use of the battery power source 2 having a voltage higher than a required voltage of the lamp, without deteriorating the lamp. Because a current to flow to the lamp 27 through the driving means 3 is limited for the definite time by means of the auxiliary driving signal generated by the driving signal generating means 5, prior to the pulse driving signal at the start of lighting the lamp 27, a rush current to flow to the lamp at the start of lighting it can be limited, thereby preventing deterioration of the lamp.
As a second aspect of the present invention, in the structure with the above first aspect, the auxiliary driving signal is of a pulse to be generated at the start of lighting the lamp 27 prior to the generation of the pulse driving signal, the pulse making the driving controlling means 4 control the lighting driving means 3, and a current to flow to the lamp 27 through the lighting driving means 3 is continuously limited for a duration of the pulse.
According to the above vehicle lamp lighting-driving apparatus, because a current to flow to the lamp 27 through the lighting driving means 3 is continuously limited for the definite time by means of the auxiliary driving signal, which is generated prior to an occurrence of the pulse driving signal at the start of lighting the lamp 27 and lasts for the definite time, a rush current to flow at the start of lighting-driving can be limited by means of the simple auxiliary driving signal, thereby preventing deterioration of the lamp without causing a large cost increase.
As a third aspect of the present invention, in the structure with the above second aspect, the driving controlling means has a first control voltage generating means to generate a first control voltage which on/off-controls the lighting driving means by the pulse driving signal and a second control voltage generating means to generate a second control voltage which limits a current, according to the auxiliary driving signal, to flow to the lamp through the lighting driving means.
According to the above vehicle lamp lighting-driving apparatus, because on/off-driving of the lighting driving means 3 and the lighting-controlling to control a current value of the lamp 27 through the lighting driving means 3 are carried out by means of the first and second control voltages generated by the pulse driving signal and the auxiliary driving signal, the lighting driving means capable of controlling voltage is provided, thereby preventing deterioration of the lamp without causing a large cost increase.
As a fourth aspect of the present invention, in the structure with the above third aspect, the lighting driving means has a single semiconductor switching element, which is on/off-driven by the first control voltage and whose conductivity can be controlled by the second control voltage.
According to the above vehicle lamp lighting-driving apparatus, because one semiconductor switching element 8 of the lighting driving means 3 is on/off-driven by the first control voltage and a conductivity is controlled by the second control voltage, it is not necessary to specially modify a structure of the lighting driving means, thereby preventing deterioration of the lamp without causing a large cost increase.
As a fifth aspect of the present invention, in the structure with either one of the above third and fourth aspects, the second control voltage generating means has a charging means to flow a charging current, according to the auxiliary driving signal, for the duration of the auxiliary driving signal and generates the second control voltage, based on the charging current.
According to the above vehicle lamp lighting-driving apparatus, because the second control voltage is generated on the basis of a charging current to be flown to the charging means 9 of the second control voltage generating means 7 for a time period corresponding to the duration of the auxiliary driving signal, the charging current does not flow over the duration of the auxiliary driving signal and also the second control voltage is not generated over the duration of the auxiliary driving signal.
The above and other objects and features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.